Controls on porosity development and the potential for CO (sub 2) sequestration or waste water disposal in the Cambrian Potosi Dolomite (Knox Group); Illinois Basin

The Midwest Geological Sequestration Consortium (MGSC), lead by the Illinois State Geological Survey, Archer Daniels Midland (ADM). Schlumberger Carbon Services, and the U.S. Department of Energy’s National Energy Technology Laboratory (DOE), is implementing a large-scale study to confirm that carbon dioxide (CO2) can be stored or sequestered permanently in the Cambrian Mount Simon Formation. Studies of other deep rock formations including the Cambrian Knox Group are ongoing to evaluate their geology and storage potential. In 2009 and 2010, Schlumberger Carbon Services drilled two wells (injection and monitoring) down to the Precambrian basement at a depth of approximately 7,000 feet. During drilling through the Potosi Dolomite in the Knox Group, circulation was lost and bit drops occurred on both wells suggesting a zone of cavernous porosity. In one of the wells, approximately 30 feet of core was cut down to this lost circulation zone. Regional studies of the Potosi Dolomite suggest this lost circulation zone may translate across the Illinois Basin implying paleo-karstification as a result of a regional unconformity. However, petrographic analyses show that porosity enhancement of the Potosi Dolomite is related to multiple events of dolomitization along fractures and specified facies. Although, later diagenetic events such as quartz precipitation occludes porosity and has been shown to translate across the Illinois Basin. Currently, petrographic and geochemical analyses are being completed to determine the paragenesis and controls on cavernous porosity development in the Potosi Dolomite throughout the Illinois Basin. The Potosi Dolomite may be a reliable and excellent reservoir for CO2 sequestration and/or waste water disposal throughout the Illinois Basin.